A constant-voltage power supply apparatus, such as a series regulator, a DC-DC converter, a switching regulator, or the like, divides an output voltage by resistors to generate a feedback voltage, and compares the feedback voltage with a reference voltage to output a constant output voltage. A power supply apparatus generating a plurality of output voltages includes voltage divider resistors dividing an output voltage, and switches a value of a portion of the voltage divider resistors by a transistor to output a different-level output voltage.
In the power supply apparatus, a voltage variation such as an overshoot or an undershoot occurs in an output voltage switching operation. Therefore, in comparison with a target voltage for switching, an output voltage may become an overvoltage, or may be primarily lower than a predetermined value.